From the command line, you can edit the /etc/sysconfig/selinux file. This file is a symlink to /etc/selinux/config. The configuration file is self-explanatory. Changing the value of SELINUX or SELINUXTYPE changes the state of SELinux and the name of the policy to be used the next time the system boots.

aptitude command - aptitude is a text-based interface to the Debian GNU/Linux package system including Ubuntu Linux

I prefer to install updates via apt-get command line:

1. gpt-get update: Update is used to resynchronize the package index files from their sources via Internet.2. apt-get upgrade : Upgrade is used to install the newest versions of all packages currently installed on the system3. apt-get dist-upgrade : Install kernel updates on a Ubuntu LTS server4. reboot

For Server Version upgrade from LTS to LTS:

sudo do-release-upgrade

NOTE: Please always make sure you test the target LTS you're being prompted to upgrade to in a LiveCD on the machine you're using to make sure everything works properly before going in for the real upgrade itself.

Cron is a daemon that executes scheduled commands. Cron reads /etc/crontab. Cron wakes up every minute, examining all stored crontabs, checking each command to see if it should be run in the current minute. When executing commands, any output is mailed to the owner of the crontab. You should use absolute path names for commands like /bin/ls. This is to insure you call the correct command.